SO that’s why. Obvious really. Those who read my letter in a previous edition will remember how, now that I have nothing to do all day I can spend a great deal of time doing exactly that.

In between bouts of complete idleness however I do go for short, if very slow walks. I find it pays to practice such skills so that in an emergency situation if there is any walking to be done then I’m your man.

The question I asked in that letter was why canal locks have one large gate upstream but two gates that meet in the middle downstream. See photo.

I have had several replies from alleged friends. Most, sadly, are unprintable but the best suggestion from Pete Harris an old (very old) chum from my previous life of toil.

Basically, according to Pete, it’s all about the forces acting on the gate/gates when they work to withstand the considerable pressure of the water when the lock is in use.

More to the point is the direction of the force of the water onto the gate and thereby into the banks of the lock. There must be something there says Pete to push back and react against the force of the water.

At this point I fell asleep but before I did I set the tape to record so I can play back and write up the rest of the explanation. So as you can see from the photograph the single upstream gate has the lock itself built into the bank to push against.

The double downhill gate however has little to push against as there is only a short length of wall and very little bank left to withstand the pressure.

So the clever bit is to use two gates that meet in the middle and crucially they meet to produce a “V” shaped barrier to the water. This then changes the angle of the forces acting on the gates.

The force will now be thrusting sideways into the bank at the angle of the gate so there is plenty of support and the gate will not fail.

It’s that simple. So why didn't I think of that. Obvious really. NOT.

For those who have cared enough to get to the end of this submission please pass go and collect £200.

Thanks Pete for your research and help with solving this problem. Keep taking your medication.

Steve Williams, Redditch